When someone tries to murder someone else, despite whether or not they are in a position of power such as the president or if they are only a citizen, that person needs to be punished. Despite the attempt having failed, that person could have easily taken a life and that can not be taken lightly.
There are some crimes that need to be taken more seriously than others. Attempted assassination of a president is a crime that should not ever be considered paid for. The inmate could be moved to a lower security, "nicer" prison, but not set free. As a matter of public policy, we must protect our president and send the message that such a crime is not forgivable.
No, this individual probably should not have been freed completely. I don't believe he belongs in prison anymore, especially if he's been reformed. But I'm not sure he's been completely reformed. Perhaps we need halfway homes where people like him, who could still possibly be a threat to others, could live without being punished but without being a risk to people.
He should stay locked up forever. When Hinkley was put away they should have made his sentence last the rest of his life. In such a hectic political season people like Hinkley should be nowhere around. He could try to take aim at another president or candidate. We should not take such risks.